Newest version of thermal comfort standard affects elevated air speeds
New requirements regarding air speeds, analysis and documentation are included in the newly published ASHRAE thermal comfort standard, ANSI/ASHRAE Standard 55-2010, Thermal Environmental Conditions for Human Occupancy.
By Craig Pearson
“The standard continues to focus on defining the range of indoor thermal environmental conditions acceptable to a majority of occupants, while also accommodating an ever increasing variety of design solutions intended to provide comfort and to respect today’s imperative for sustainable buildings,” said Stephen Turner, of the Standard 55 Committee.
The standard specifies the combinations of indoor thermal environmental factors and personal factors that will produce thermal environmental conditions acceptable to a majority of the occupants within the space.
Standard 55 incorporates recent research innovations such as the use of elevated air speeds to widen the acceptable range of thermal conditions. The standard previously allowed modest increases in operative temperature beyond the Predicted Mean Vote/Percentage of Persons Dissatisfied (PMV/PPD) limits as a function of air speed and turbulence intensity.
The 2010 standard, according to ASHRAE, also includes a new method for determining the cooling effect of air movement above 0.15 m/s (30 fpm). This allows ceiling fans, or other means to elevate airspeed, to provide comfort at higher summer temperatures than were previously permissible. New provisions based on field study research allow elevated air speed to broadly offset the need to cool the air in warm conditions, replacing requirements that originated primarily from climate chamber studies.
Another revision makes clearer the mandatory minimum requirements for analysis and documentation of a design to show that it meets the standard’s requirements. In addition, a compliance form for documentation of design is included in an informative appendix. This compliance template mirrors the United States Green Building Council’s LEED template for the thermal comfort design credit in LEED New Constuction-2009, which ASHRAE says simplifies the LEED credit template for the designer during a project.
ASHRAE says the 2010 version of the standard includes improved and expanded graphics that better guide users of the standard in simple applications. Improvements to the SI and IP versions of the traditional “comfort zone” chart include enlargement, clarification and notes to aid users of the standard.
Standard 55 combines Standard 55-2004 and the ten approved and published addenda to the 2004 edition into one easy-to-use, consolidated standard.
The cost of Standard 55 is $69 ($59 for ASHRAE members). To order, visit www.ashrae.org/bookstore.